package com.java.lock;

import javax.security.auth.kerberos.KerberosTicket;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * @author wangning
 * @date 2023/5/15 16:04
 * 多个线程同时读一个资源类没有问题，所以为了满足并发量，读取共享资源应该可以同时进行
 * 但是
 * 如果有一个线程想去写共享资源，就不应该再有其他线程可以对该资源进行读或写
 * 小总结：
 * 读读能共存
 * 读写不能共存
 * 写写不能共存
 * <p>
 * 写操作：原子+独占
 */
public class ReadWriteLockDemo {
    public static void main(String[] args) {
        MyCache myCache = new MyCache();

        for (int i = 0; i < 5; i++) {
            final int tempInt = i;
            new Thread(() -> {
                myCache.put(tempInt + "", tempInt + "");
            }, String.valueOf(i)).start();

            new Thread(() -> {
                myCache.get(tempInt + "");
            }, String.valueOf(i)).start();

        }
    }
}

class MyCache { //资源类
    private volatile Map<String, Object> map = new HashMap<>();

    //    private Lock lock = new ReentrantLock();
    private ReentrantReadWriteLock rwlock = new ReentrantReadWriteLock();

    public void put(String key, Object value) {
        rwlock.writeLock().lock();

        System.out.println(Thread.currentThread().getName() + "\t 正在写入" + key);
        try {
            TimeUnit.MILLISECONDS.sleep(300);
            map.put(key, value);
            System.out.println(Thread.currentThread().getName() + "\t 写入完成" + key);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            rwlock.writeLock().unlock();
        }

    }

    public void get(String key) {
        rwlock.readLock().lock();
        System.out.println(Thread.currentThread().getName() + "\t 正在读取" + key);
        try {
            TimeUnit.MILLISECONDS.sleep(300);
            Object res = map.get(key);
            System.out.println(Thread.currentThread().getName() + "\t 读取完成" + res);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            rwlock.readLock().unlock();
        }

    }

    public void clearMap() {
        map.clear();
    }
}











